Conventional low density polyethylene (LDPE) has good processability; however, when used in film, extrusion coating and/or extrusion lamination applications, improved melt strength is still desired. In addition, there is a need for such polymers that have improved adhesion to cellulosic based substrates, such as paper and paperboard, or polar and other substrates, such as aluminum foil or metalized films such as OPP (oriented polypropylene), metalized PET (polyethylene terephthalate) and the like.
Ethylene-based polymers used for coatings and films are disclosed in the following references: International Publication Nos. WO 2011/071843, WO 1991/18944; U.S. Pat. Nos. 5,178,960, 3,860,538, 4,714,741, 6,558,809, 4,962,164, 3,676,401; GB 1448062; EP 0230143B1; Ward et al., Ethylene-Carbon Monoxide Extrudable Adhesive Copolymers for Polyvinylidene Chloride, June 1988 Tappi Journal, pp. 140-144; Scott et al., Degradable Polymers, Principles and Applications, Chapter 8: Ethylene-carbon monoxide copolymers, pp. 156-168, Chapman and Hall (1995). See also International Application PCT/US13/076423 (now WO2014/105608), and U.S. Provisional 62/018,050 filed Jun. 27, 2014.
U.S. Pat. No. 6,407,191 discloses the use of carbonyl group containing chain transfer agents to obtain improved polymer processing and performance properties in extrusion processes and applications. The level of carbonyl group containing compound (ketones and aldehydes are claimed) ranges from 0.1 to 0.5 wt %. Production of high molecular weight polymers will restrict the level of ketonic or aldehydic chain transfer agents to be used to control the melt index, and therefore the maximum level which can be incorporated in the polymer to 0.5 wt %.
U.S. Publication No. 2008/0242809 and International Publication Nos. WO 2007/110127, WO97/45465, WO 2012/057975 and WO 2012/084787 describe using various multifunctional components to broaden molecular weight distribution (MWD) and/or modify the rheological properties, for making a copolymer suitable for extrusion coating applications, among others. The multifunctional components include, among others, di- and/or higher functional (meth)acrylates, a bifunctional α,ω-alkadienes, diunsaturated comonomers containing divinyl ether and monomeric chain transfer agents (CTAs). International Application No. PCT/US13/029881 discloses an ethylene-based polymer formed from reacting ethylene and at least one rheology modifying agent comprising an “alpha, beta unsaturated end” and a “C—C double bond end,” wherein the reaction takes place in the presence of at least one free-radical initiator.
However, as discussed above, there remains a need for new ethylene-based polymers that have higher melt strengths, and improved adhesion to substrates. These needs have been met by the following invention.